1. Field of the Invention
The invention relates to a power converter, and more particularly to a power converter with primary-side feedback control and a voltage control method thereof, which are suitable for operation in continuous conduction mode, discontinuous conduction mode, or boundary conduction mode.
2. Description of the Related Art
Power converters have been commonly used in power circuits of various electronic devices. As shown in FIG. 1, the known voltage converter 900 employs a secondary side feedback control architecture that requires many circuit elements, resulting in great circuit size and complexity in circuit design. In addition, a current transfer ratio (CTR) of a low-cost optical coupler 910 of the power converter 900 may severely decay with temperature and time, thereby resulting in low reliability of the circuit. Therefore, some power converters employ primary side regulation (PSR) techniques to simplify the circuit and reduce the cost.
However, under the conventional PSR control, the power converter operates in a discontinuous conduction mode to detect voltage waveform of the primary side winding to control the transistor duty cycle for stabilizing an output voltage, which is only suitable for low-power applications (under 15 W). In other words, when the output load current is large, the output voltage may have large variations that may adversely affect voltage regulation, thus being unable to satisfy requirements of high-power voltage converters.